Process of making plywood



H. v. DUNHAM 1,873,827

PROCESS OF MAKING PLYWOOD Filed Jan. 28, 1951-- v GLUE [761 A |ES 1 GLUE ASSEMBLY COLD PLATEN' F162 E ::1B P IE COLD PRESS/N6 FOR CO D PLATE L N AT LEAST THEN PAR T/ALL) om PLVWOOD //v ORV/N6 ROOM PLATEN F163 GLUE B L ES [Ii-EMT;

INTERVALS ATEN o/vu WHILE HOT INVENTOR. hCMDUNHAMv BY rww ATTORNEY Patented Aug. 23, 1932 PATENT OFFICE- HENBY V. DUNHAM, OF BAINBRIDGE, NEW YORK PROCESS OF MAKING PI-YWOOD Application filed January 28, 1981. Serial No. 511,932.

The present invention relates to improvements in making plywood, and has for its object to improve the pro rties of the final plywood, without increaslng the expense of manufacture, or without substantially increasing this expense.

An important object of the invention is to increase the water resisting qualities of the glue when used, especially in making plywood.

For gluing up pl wood the cold process has been heretofore argely used, partlcular- 1y with glues such as those made from casein or seedmeal or mixtures of the same, containing an alkaline material which will serve as a solvent for the proteids of the seedmeal, or for the casein, and when water-resistance was required it has -.been the usual practice to employ considerable quantities of lime or other alkaline earth compound of a basic nature, such as magnesium oxide or hydroxide. The glue, prepared according to any of the well known processes or formulas has been' mixer. with about two or two and a half parts of water to one part by weight of the commercial dry glue, and the usual procedure in making three ply plywood has been to apply the glue to both s1des of the center piece or core, then to apply the face veneers upon the wet cores, and the usual practice has been in many of the mills, to continue to make up the panels for about twenty-five minutes, then the pile of glue-spread anels is placed under pressure, sa in a hydi'aulic press, for twelve to twentyour hours. The

pressure is then released and the panels are stacked up in a drying room for days (usually three to ten days) to season and dry out,

prior to finishing or shipping the same. In making up plywood there are many well known advantages in using casein glues or seedmeal glues or casein and seedmeal glues or blood albumen glues or blended glues containing a plurality of these materials, in place of ordinary animal glue, fish glue, hide glue and the like.

Hot plate gluing is of course well known, and it is also Well known that when the panels are pressed hot there is an increased tendency for the glue to come through the face veneers and stain the faces of the panels. This is one of the reasons why cold gluing, of the character above described has been more commonly used in the prior art. Another objection to the hot glulng is that very often blisters or spots are formed where there is no adhesion of the veneers to the core in the glued up panels made by the hot pressing method. It is believed that the blisters may be largely due to the development of steam so in'the glue line, the steam expanding and separating the pieces of veneer from the core,

to some extent, thereby preventing adhesion of the veneer to the core.

In accordance with the present invention I 05 may proceed according to the well accepted method above described, down to the step of cold pressing. I find it unnecessary and even inadvisable, in the present invention, to press for nearly as long a time as in the standard 7 process above described, and ordinarily L cold-press the material only until the glue has set or hardened suflicient-ly to allow of safely handling of the plywood. For ordinary purposes, instead of allowing the pile of glue- 7 spread panels to remain in the press for twelve to twenty-four hours, they may be taken out of the press after about four to eight hours. They may be then stacked up in the usual manner for a partial drying, of 1 several hours or if desired up to one or two days or longer in some cases, or this operation can in some cases be omitted if desired. Such drying should not be complete. Then the pressed plywood is subjected to a suitable 5 heat treatment, for example by being passed between strongly heated rollers, or by being pressed for a few minutes in a hot platen press, or even they can be passed through a heated oven or a hot drying room, during which operation the wood itself is heated up to a temperature of preferably about 225 F.

to 260 F.

When using a continuous dryer of a type like the well known Coe dryer, it is important that the glue line should not contain such quantities of moisture as to cause too great an expansion in the line and thus cause blisters, when the heat is applied. This difiiculty may be overcome by using a lower heattemperature and a longer exposure in the heating device or by delaying the heating process for a time until more of the moisture has evaporated from the panels or one may heat such high-moisture panels by means of a dryer having successive stages in the temperature so that as the panels are first heated the temperature is a little below 212 F. in the first part of the drying, and as the panel moves forward through the dryer, the temperature is gradually increased up to the final temperature desired.

Another method. which may be employed is to delay putting the panels through the heating process for a longer period of time after the panels come from the cold pressure, such period of time being sufiicient to allow enough moisture to evaporate from the glue to permit of the heating process without causing blisters.

Because of the great difference existing in different types of construction of panels as to the various thicknesses of core and veneer used and to the different kinds of wood employed in making such panels, there is no set rule to go by as to what the moisture content must or may be. To avoid this blistering I have found that the best way to determine this point is to make preliminary tests of single panels or a sample panel from time to time until it is found that the panels have aged or dried sufiiciently so that the panels can be put through a dryer like the (Joe dryer or like the Merritt plate dryer or any other, to secure the necessary temperature without causing blisters in the resulting panel.

The pressure employed in the cold press may be that ordinarily used, say 125 to 175 pounds or more. It is very advisable to get the assembled plywood into the press within 15 or 20 minutes or say within half an hour after the application of the glue to the cores and the assembly of the face veneers and back veneers thereupon.

It is of course understood that there is a sort of hydrolytic decomposition going on in the liquid glue, which commences as soon as the dry glue base is mixed with the water, this decomposition goes on in the glue kettle itself, and continues during the step of applying the liquid glue to the core, and continues while the plywood is in the press and even during the subsequent drying of the veeners or finished plywood, but on account of the fact that the water is rapidly absorbed from the liquid glue by the core and surface veneers, the decomposition seems to go on more slowly in the press, than in the glue-mixing kettle, and probably still more slowly in the subsequent drying operation, the rate of such decomposition very considerably slowing d wn as the water is removed from the glue. t also will be understood that the staining operation is a somewhat progressive action, and the sooner the drying is completed (other thingsbeing lime which glues were as follows (parts are by weight) 70 ground casein 12 hydrated lime 5 sodium fluoride 5 tri-sodium phosphate 3 sodium carbonate 65 ground casein 15 hydrated lime 5 sodium fluoride 8 tri-sodium phosphate These examples are only given by way of illustration and the amounts of chemicals used may be varied to quite a large extent and it is of course understood that other substances such as fillers or other protein substances may be used in connection with these glues without departing from the scope of this invention.

These glues were each dissolved in cold water, using two parts of water to one part of the dry glue base. After mixing for 20 minutes the glue was ready for use. The glue was applied to the cores by the usual double roller glue spreader, the face and back veneers then applied to this core, (the grain of the wood in the core being at right angles to the grain of the outer veneers). Two lots of panels (exactly alike, same wood, same glue, same spread, etc.) were so assembled from each one of these glues, and each lot was then placed in a, hydraulic press under a pressure of 150 pounds per square inch.

Ewpcfiment A One lot of these panels were removed after 24 hours in the press, and these were then stacked and dried in a warm room for seven days, and were tested for wet and dry strength in the usual manner. (This experiment represents conventional cold glue process.) The wet strength and dry strength of the panels glued up with the first glue, are given below in Table No. 1 in column A.

Empefiment B The other lot of the panels (made exactly like the lot above referred to and with the same glues, from the same mixes) were allowed to stand in the'press, for 24 hours, and

were then removed, and each panel was put into a Gee dryer and heated. In a Coe dryer, the plywood passes through a long heated chamber, and between press rolls, at intervals. These panels were then taken out and stacked up and dried for seven days and tested. (This experiment represents one example of my improvement as covered herein.) The results (using the first glue given above) are stated in the Table No. 1 below in column B.

It will be understood that during the 24 hours pressing, in each case, there was no substantial evaporation of water. Practically the only drying of the glue during this step is by absorption of the water into the wood.

In the following Table 1 I give the results of the tests above referred to (12 panels in each test) with the first glue, as above described.

A B n. it? "$32 2%; ll; D atrengt g ry Averago---483 546 lbs Low .155 240 lbs Wetstrength.{Hlgh .170 290 lbs. Average-..l60 266 lbs.

These figures show a very great improvement by the process of the present case, over the conventional process, and especially important where high wet strength is required.

In rather exhaustive factory tests made on a commercial scale panels made as described herein were after having been pressed in the cold press for 24 hours, removed and a part of the panels allowed to dry under ordmary factory conditions in the air. Other portions of the same panels were treated in a Coe dryer. In this case the coils in the Coe dryer showed a steam pressure of 75 pounds per square inch and the temperature in the dryer was 260 F. The panels were allowed 15 minutes in running through this dryer, Another set of panels were treated in the Merritt hot plate dryer. The pressure in the plates of the Merritt dryer showed 40 pounds steam pressure equal to approximately 286 F. The pressure used in the cold gluing of these panels prior to this heat treatment was 125 lbs. per square inch.

An object of the present invention is to give the glue line in the glued up pressed panel a heat and pressure treatment or at least a heat treatment prior to the glue line havin become completely dried out. In fact I pre er to give this heat treatment as soon after the panels have been glued up and cold pressed as possible without causing blisters. Especially where a hot press is to be used, the cold press treatment can be discontinued as the glue has set sufiiciently to enable the panels to be handled safely. If the heat treatment is to be efiected by a hot blast of air, without pressure, the cold press operation may be continued for at least about '6 to 8 hours. The drying by hot blast does not usually produce as water-proof results as when the hot press is employed, biit even with the hot blast treatment hi her wet and dry strength may I be expected t an when the former cold pressing method is used followed by drying for a week or so in a room at ordinary atmospherictem erature.

T e process of the present case improves the glue joint as to both wetand dry strength, particularly wet strength.

After taking out o f\the cold press the heat Tt will be understood that in all of the air drying operations above referred to it is customary to stack up the plywood in such a way as to allow good ventilation of the same, for example by placing thin sticks between the successive pieces of plywood.

The main idea is to heat the glue line one way or another prior to its having given up so much moisture as to fail to react and produce improved results when heat is applied. I have heat-treated panels which were several weeks old and which were well dried out and these heated panels so aged, were not improved whatever by the heat treatment.

The annexed drawing is a diagrammatic view of the process, and it is understood that while certain structural elements of apparatus are shown therein, these are merely by wa of example.

ig. 1 shows the core A having glue applied at the bottom and top of the same, and

above and below this respectively are the top a veneer N and the bottom veneer (7.

Fig. 2 illustrates the step of cold pressing the assembled plywood between two cold platens, which step is continued for at least four hours. The cold pressed plywood is then partially dried (and only partially) in a drying room in the usual manner.

Fig. 3 shows one form of hot pressing, with steam heated platens, but it will be understood that various other methods can be employed.

I claim 1. A process of making plywood which a so ' comprises coating cores wit heat until the glue line is sufficiently comprises heat-treating glued and wood while the glue in the glue line still ithe panels from the press, allowing the lue contains some moisture and continuing1 the and until the same is more water-resistant than could be obtained by the use of the same line 'still contains somemoisture.

lywood which a casein-contaimng alkaline glue in a li uid state, assembling veneer on same, cold pressing the assembled plywood, which pressing is continued for at least long enough for the glue 4. A process of making to set, and then heating the plywood while the glue is still somewhat moist;

5. A process of making plywood which 'comprises coating cores with an alkaline seedmeal and casein blend glue in a li uid state, then, within half an hour, assemb ing veneer on same, cold pressing the assembled lywood, which pressing is continued for at east about four hours, and thereafter heating the plywood while the glue still contains zome moisture until the glue is sufiiciently The herein described process which ressed plywood after the glue has set an dried enough to permit safe handling of the plywood, and then heating the plywood while a substantial amount of water originally applied in the liquid glue is still contained in the plywood.

7. The modification of the process of gluing up plywood with an alkaline proteincontaining liquid glue, which comprises subjecting the glue in the plywood, after setting, and after only a partial absorption of the water of the glue by the wood, to a heat treatment sufiicient to increase the water-resistance of the dried plywood.

8. That modification of'the process of gluing up plywood with an alkaline proteincontaining l i uid glue, which comprises subjecting the g ue in the plywood, after setting, and after only a partial absorption of the water of the glue by the wood, to a hot I press treatment, and thereafter drying the plywood.

9. A process of making plywood which comprises coating cores with an alkaline liquid proteinaceous glue, assembling veneer on the same, cold pressing the assembled plywood until the adhesion of the glue line is suflicient to permit of removing the panels from the press without separation, removing 6. and then heatin 'els from the press and then heating the plyline of-such panels to only ogartiallly so 0 tained the plywo substantially as escribed.

10. process of making plywood which t'comprlses coating cores with an alkaline liquid proteinaceous glue, assembling veneer on same, cold pressing the assembled plywood until the ad esion of the glue line is sufiicient ;to permit of removing the panels from. the

press without separation, removing the paned. whereof I aflix m si ature.

HENRY V. D AM.

wood so obtained substantially as descri In testimony 

